1. Field of the Invention
The present invention relates to a spacer assembly for use in a magnetic head, and to a magnetic head and more particularly to a magnetic head which has a pair of magnetic core assemblies arranged in parallel in a direction across the width of the track, and a spacer assembly sandwiched by the core assembly. The present invention also relates to a method for fabricating a spacer assembly for use in a magnetic head and to a method for manufacturing: such a magnetic head.
2. Description of the Prior Art
Floppy disk drives having capacities of 1 to 2 MB have been prevailing. As a result of incessant efforts for obtaining floppy disk drives with larger capacities floppy disk drives having capacities of even above 10 MB (Mega-Bits) have recently been commercialized.
One mega bits floppy-disk drives (1 MB FDD) have a maximum line recording density of 9.7 kilobit per inch (KBPI), and a track density of 135 track per inch (TPI). To achieve a capacity of above 10 MB, the floppy disk drivemust have a line recording density of 35 KBPI or more and a track density of 405 TPI to 1,000 TPI, or more, in other words both the line recording density and the track density of the floppy disk drive must be at least 3 times as high as those of a 1 MB floppy disc drive.
Here, it must be taken into consideration that compatibility between higher level (larger capacity) and lower level (smaller capacity) devices must be maintained in general use of floppy disk drives in order to maintain compatibility of softwares and data. For example, a 2 MB device reading/writing a 3.5 inch floppy disk has read/write compatibility with 1 MB device and can read/write in a format which corresponds to that of the 1 MB device. Likewise, a 4 MB device has read/write compatibility with 1 MB and 2 MB devices. Also, devices with capacities of 10 MB or more are required to record and reproduce information in formats used by the lower level counterparts, i.e., must have R/W compatibility with the lower level ones. Floppy disk drives with capacities of 1 to 4 MB share the same track density of 135 TPI so that the read/write compatibility can be maintained naturally. In contrast to this, 10 MB or more floppy disk drives with higher track densities can read out signals recorded with low level devices with lower track densities but cannot write in formats corresponding to those of the lower level devices. This results in an insufficient compatibility of softwares or programs and data with conventional ones.
To meet the requirement for the compatibility between the floppy disk drives of different track densities, the use of a composite magnetic head has been proposed which includes a magnetic core assembly of the tunnel erasing type for use in 1 to 2 MB devices and a magnetic core assembly for use in devices with capacities of 10 MB or more and different track densities, arranged in parallel via a spacer so that recording and reproducing of information can be performed. The structure of such a conventional composite magnetic head will be described with reference to FIGS. 1 to 3.
FIG. 1 is an exploded perspective view showing the construction of the main body of a magnetic head of the aforementioned type. In FIG. 1, reference numeral 1 denotes a front core assembly (hereafter, abbreviated as "core assembly"), which is constructed as an assembly including a magnetic core 2 for recording and reproducing at a track density of 135 TPI (hereafter, referred to as "recording and reproducing core") and a magnetic core 4 for performing tunnel erasing (hereafter referred to as "erasing core"), with their front cores being coupled together via a spacer 6.
The recording and reproducing core 2 has an L-shaped front core 2a and an I-shaped front core 2b coupled with each other via a recording and reproducing gap 3, and a back core 15 connected to the rear ends (lower ends in FIG. 1) of the front cores 2a and 2b.
The erasing core has an L-shaped front core 4a and an I-shaped front core 4b coupled with each other via erasing gaps 5 and 5', and a back core 16 connected to rear ends (lower ends in FIG. 1) of the front cores 4a and 4b.
On the other hand, reference numeral 21 denotes a core assembly which includes a recording and reproducing core 22 for a higher track density (e.g., 405 to 1,000 TPI) and a back core 29 connected to the bottom end of the recording and reproducing core 22. The recording and reproducing core 22 has an L-shaped front core 22a and an I-shaped front core 22b, which have thin films 24 respectively of predetermined thicknesses made oil a high saturation flux density material such as a Fe-Al-Si alloy formed by a thin film formation technique such as sputtering or vapor deposition on the butt surfaces of the front cores 22a and 22b between which bunt surfaces a recording and reproducing gap is to be formed. Then a nonmagnetic thin film is formed on each of the thin films 24 on the front cores 22a and 22b. The front cores 22a and 22b are butted together via the nonmagnetic thin film serving as the recording and reproducing gap 23.
On both sides of the upper end of the recording and reproducing core are connected rectangular spacers 25a and 25b made of a nonmagnetic material such as a ceramic, a nonmagnetic ferrite or glass and serving as a sliding surface. Thus the core assembly 21 is constructed.
A spacer assembly 40 has a T-shaped form so that it can correspond to the upper end portions of the sides of the core assemblies 1 and 21, and to the connecting surfaces 7a and 8a of sliders 7 and 8, respectively, described later on. The spacer assembly 40 comprises a shield plate 41 made of a magnetic material and a pair of spacers 42 each made of a nonmagnetic material, sandwiching the shield plate 41. Thus, the spacer assembly is of a laminated structure.
In the assembly process of a magnetic head main body 31 shown in FIG. 2, the core assemblies 1 and 21 are arranged so as to sandwich the spacer assembly 40, and the sliders 7 and 8, which are nonmagnetic, sandwich the resulting composite and the elements are bonded with an adhesive or by a conventional glass welding process.
The sliders 7 and 8, together with the core assemblies 1 and 21 and the spacer assembly 40, slide on a magnetic disk or a floppy disk (not shown) so as to stabilize the sliding of the both core assemblies 1 and-21 on the floppy disk, and to protect the core assemblies 1 and 21. The sliders 7 and 8 are made of a ceramic or the like, and are formed with notches 7b and 8b, respectively, thus taking block-like shapes having L-like cross sections, respectively, and are joined to opposite sides of the front core assemblies 1 and 21 at junction surfaces 7a and 8a which are each formed in a T-shaped form as unnotched portions.
After the sliders are attached, a coil bobbin 9 around which a recording and reproducing coil 10 is wound is mounted on the front core 2a of the core assembly 1 while a coil bobbin 12 around which a coil 13 is wound is mounted on the front core 4a of the front core assembly 1. The coil bobbin 12 has a terminal portion 12 provided integrally therewith in which terminals 12d made of a metallic material are provided as by insertion molding or pressing-in, to which coil ends 13a of the coil 13 are soldered.
Subsequently, the back cores 15 and 16 coupled together via a spacer 17 are joined to the lower ends of the legs of the front cores 2a, 2b, 4a and 4b of the front core assembly 1 to form a magnetic circuit for the magnetic core of a lower level device (lower level core).
Likewise, a coil bobbin 27 around which a recording and reproducing coil 28 is wound is mounted on the front core 22a of the core assembly 21 and the back core 29 is connected to the bottoms of the front cores 22a and 22b to form a magnetic circuit for the magnetic core of an upper level device (upper level core).
The slider 8 is formed with a groove 8e, in which a terminal assembly 30 having a terminal body 30a and a plurality of terminals 30b provided therewith is inserted and fixed. The coral ends 10a and 28a of the coils 10 and 28, respectively, wound around the coil bobbins 9 and 10, respectively, are connected to the terminals 30b to form a magnetic head main body 45 shown in FIG. 2.
Then, as shown in FIG. 3, the magnetic head main body 45 shown in FIG. 2 is fixed on a support plate 19 made of stainless steel, beryllium copper or the like, and the terminals 12d and 30b are connected to a flexible print board 20 connected to the support plate 19. Thus a magnetic head 47 is constructed.
The magnetic head 47 thus constructed is mounted on a head carriage in a floppy disk drive (not shown) by fixing the support plate 19 thereon. Thus, the top surface of the magnetic head main body, i.e., the top surfaces of the front core assemblies 1 and 21, the spacer assembly 40 and sliders 7 and 8, together form a disk sliding surface 32, which slides on a floppy disk, thereby performing recording and reproduction. Upon recording and reproduction, the recording and reproducing core 2 and the erasing core 4 of the core assembly 1 or the recording and reproducing core 22 of the core assembly 21 is selected appropriately in accordance with the track density of the floppy disk to be written or read, which makes it possible to achieve R/W compatibility between upper and lower level devices with different track densities
However, the conventional composite magnetic head 45 suffers a problem of crosstalk which is induced by magnetic leakage between the front core assemblies 1 and 21, because they are disposed in close vicinity via the spacer assembly 40 as shown in FIGS. 1 and 2.
For example, consider the case where a higher density disk (for example, 405 TPI) is replayed by a higher level floppy disk drive. In this case, the reproduction of the higher density disk is carried out by the recording and reproducing gap 23 of the core assembly 21. At the same time, however, the recording and reproducing gap 3 of the core assembly 1 which is provided for a lower density disk (for example, 135 TPI tunnel erasing type) and is placed in close proximity of the core assembly 21 will reproduce a plurality of tracks of the higher density disk. This will cause the flux through the core assembly 1 to leak into the front core assembly 21, thereby inducing crosstalk.
The crosstalk thus induced will degrade the reliability of the reread data, and presents an important problem in constructing floppy disk drives. In addition, once-crosstalk takes place, the core efficiency during the recording or reproduction reduces. This will result in an increase in current to be applied to the coil 28 in order to carry out sufficient recording, a decrease in the margin of the reproduced signal, or a decrease in resistance against noise, which requires a change of circuitry of the floppy disk drive or the design modification thereof.
The crosstalk would be prevented by the use of a construction in which the spacer assembly 40 comprises a shield plate 41 made of a magnetic material and a pair of spacers 42 each made of a nonmagnetic material and sandwiching the shield plate 41. However, this causes another problem. That is, because the core assemblies 1 and 21 are disposed in close vicinity one to another, the insertion of the shield plate made of a magnetic material leads to an increase in the leakage magnetic resistance to increase the inductances of the recording and reproduction cores 2 and 22, respectively. Increased inductances cause severe problems particularly when recording and reproduction is to be performed by the upper level core in a format for an upper level device having a capacity of 10 MB or more, since the recording frequency is high and the transmission rate is also high. For example, higher inductances cause problems such as retarding the elevation of recording wave forms.
To avoid the problems, a possible countermeasure will be to reduce the number of winding of the coil 28 to decrease the inductance. However, reduction in the number of winding of the coil results in reduction in the reproduction power, which then causes problems of noise and of necessity of increasing the level of the amplifier.